Methods, systems and media for controlling a toolface of a downhole tool

ABSTRACT

Methods, systems, and computer-readable media for controlling a toolface of a downhole tool are described. The toolface of the downhole tool, and a toolface setpoint, are determined. Based on the toolface and the toolface setpoint, a toolface error is determined. Based on the toolface error, one or more drilling parameter setpoints are selected from among multiple drilling parameter setpoints. The selected one or more drilling parameter setpoints are adjusted. The adjusted one or more drilling parameter setpoints are inputted to one or more drilling controllers for controlling the toolface of the downhole tool.

TECHNICAL FIELD

The present disclosure relates to methods, systems, andcomputer-readable media for controlling a toolface of a downhole tool.

BACKGROUND

During oil and gas drilling, a drill bit located at the end of a drillstring is rotated into and through a formation to drill a wellbore. Oneform of drilling is directional drilling, in which the drill string hasa slight bend near its distal end. During directional drilling, it iscommon practice to alternate between sliding and rotating. When sliding,the drill string is rotated to a particular orientation, and thendrilling proceeds with the drill string maintained in this constantorientation, allowing the driller to alter the direction of the wellborevia the bend in the drill string. When rotating, the entire drill stringis rotated, allowing the driller to drill forward in a straight linefrom the last slide. The driller alternates between rotating andsliding, to steer the wellbore as desired.

During the sliding portions of the drilling operation, the driller needsto ensure that the toolface (e.g. the orientation) of a mud motor/bentsub connected to the downhole tool is properly set, to point, using thebend in the mud motor, the drill bit in the desired direction.

SUMMARY

According to a first aspect of the disclosure, there is provided amethod of controlling a toolface of a downhole tool, comprising: when adrill bit is off-bottom relative to a wellbore: determining a totalamount of rotation to be introduced to a drill string connected to thedrill bit; and performing a first toolface control operation comprisingrotating the drill string by an off-bottom amount of rotation; measuringa differential pressure; determining, based on the measured differentialpressure exceeding a threshold, that a touchdown condition has been met;and in response to determining that the touchdown condition has beenmet, performing a second toolface control operation comprising furtherrotating the drill string by an on-bottom amount of rotation, whereinthe total amount of rotation is equal to a sum of the off-bottom andon-bottom amounts of rotation.

Rotating the drill string may comprise adjusting a rotary drive unitposition setpoint corresponding to a desired position of a rotary driveunit operable to rotate the drill string.

The rotary drive unit position setpoint may comprise a top driveposition setpoint. The rotary drive unit may comprise a top drive.

The desired position of the rotary drive unit may comprise an angularposition of the rotary drive unit or a midpoint or a neutral point of arange of angular positions within which the rotary drive unit isoscillated.

Determining the total amount of rotation may comprise: determining adifference between a differential pressure setpoint and an initialdifferential pressure; and determining the total amount of rotationbased on the determined difference.

The total amount of rotation may be equal to(DiffP_Setpoint−DiffP)*ReactiveT_Factor, wherein DiffP_Setpoint is thedifferential pressure setpoint, DiffP is the initial differentialpressure, and ReactiveT_Factor is a constant.

The method may further comprise, before performing the first toolfacecontrol operation, determining an initial differential pressure; anddetermining that the measured differential pressure has exceeded thethreshold by: determining a differential pressure setpoint; anddetermining that the measured differential pressure is greater than apredetermined fraction of the differential pressure setpoint minus theinitial differential pressure.

The off-bottom amount of rotation may be at least as large as theon-bottom amount of rotation.

Performing the first toolface control operation may comprise rotatingthe drill string by the off-bottom amount proportionally to increasingdepth of the drill bit.

The method may further comprise, before performing the first toolfacecontrol operation, rotating the drill string by an initial amount ofrotation.

The initial amount of rotation may correspond to a difference between aninitial toolface of the downhole tool and a toolface setpoint.

The method may further comprise: before performing the first toolfacecontrol operation, determining an initial toolface of the downhole tool;and determining a toolface setpoint, wherein the initial toolface andthe toolface setpoint define an expected toolface range; and furtherrotating the drill string if the toolface of the downhole tool isdetermined to be outside of the expected toolface range.

The method may further comprise, if the toolface of the downhole tool isdetermined to be outside of the expected toolface range, then redefiningthe expected toolface range based on the toolface setpoint and thetoolface determined to be outside of the expected toolface range.

Performing the second toolface control operation may comprise furtherrotating the drill string by the on-bottom amount proportionally toincreasing differential pressure.

The method may further comprise: after performing the second toolfacecontrol operation, determining that a depth of the drill bit correspondsto a depth of the wellbore; and in response to determining that thedepth of the drill bit corresponds to the depth of the wellbore,performing a third toolface control operation comprising furtherrotating the drill string.

Performing the third toolface control operation may comprise: increasinga differential pressure setpoint such that the differential pressuresetpoint corresponds to a reactive pressure; and further rotating thedrill string based on the increased differential pressure setpoint.

The method may further comprise, after performing the second toolfacecontrol operation: determining a toolface error based on a differencebetween the toolface of the downhole tool and a toolface setpoint;adjusting, based on the toolface error, one or more drilling parametersetpoints; and inputting the one or more adjusted drilling parametersetpoints to one or more drilling controllers for controlling thetoolface of the downhole tool.

Adjusting the one or more drilling parameter setpoints may comprise:selecting, based on the toolface error, one or more drilling parametersetpoints from among multiple drilling parameter setpoints; andadjusting the selected one or more drilling parameter setpoints.

Adjusting, based on the toolface error, the one or more drillingparameter setpoints may comprise adjusting the one or more drillingparameter setpoints with one or any combination of: a proportionalcontroller; an integral controller; and a derivative controller.

According to a further aspect of the disclosure, there is provided amethod of controlling a toolface of a downhole tool, comprising:determining the toolface of the downhole tool; determining a toolfacesetpoint; determining, based on the toolface and the toolface setpoint,a toolface error; selecting, based on the toolface error, one or moredrilling parameter setpoints from among multiple drilling parametersetpoints; adjusting the selected one or more drilling parametersetpoints; and inputting the adjusted one or more drilling parametersetpoints to one or more drilling controllers for controlling thetoolface of the downhole tool.

The toolface error may be indicative of one or more of: a magnitude of adifference between the toolface and the toolface setpoint; and adirection of a difference between the toolface and the toolfacesetpoint.

The one or more drilling parameter setpoints may comprise one or moreof: a weight-on-bit (WOB) setpoint; a differential pressure setpoint; arate of penetration (ROP) setpoint; and a rotary drive unit positionsetpoint.

The one or more drilling controllers may comprise one or more of anautomated drilling unit and a rotary drive unit controller; andinputting the adjusted one or more drilling parameter setpoints to theone or more drilling controllers comprises: inputting the adjusted oneor more drilling parameter setpoints to the automated drilling unit ifthe one or more drilling parameter setpoints comprise one or more of aWOB setpoint, an ROP setpoint, and a differential pressure setpoint; andinputting the adjusted one or more drilling parameter setpoints to therotary drive unit controller if the one or more drilling parametersetpoints comprise a rotary drive unit position setpoint. The rotarydrive unit may comprise a top drive, and the rotary drive unit positionsetpoint may comprise a top drive setpoint.

If the toolface error is indicative that the toolface setpoint islocated in a counter-clockwise direction relative to the toolface of thedownhole tool, then selecting the one or more drilling parametersetpoints may comprise selecting one or more first drilling parametersetpoints from among the multiple drilling parameter setpoints.

If the toolface error is indicative that the toolface setpoint islocated in a clockwise direction relative to the toolface of thedownhole tool, then selecting the one or more drilling parametersetpoints may comprise selecting one or more second drilling parametersetpoints from among the multiple drilling parameter setpoints.

If the toolface error is indicative that the toolface setpoint islocated in a counter-clockwise direction relative to the toolface of thedownhole tool, then adjusting the selected one or more drillingparameter setpoints may comprise adjusting one or more of a WOBsetpoint, an ROP setpoint, and a differential pressure setpoint.

If the toolface error is indicative that the toolface setpoint islocated in a clockwise direction relative to the toolface of thedownhole tool, then adjusting the selected one or more drillingparameter setpoints may comprise adjusting a rotary drive unit positionsetpoint.

If the toolface error is indicative that a difference between thetoolface setpoint and the toolface of the downhole tool is greater thanabout 90 degrees, then adjusting the selected one or more drillingparameter setpoints may comprise adjusting: one or more of a WOBsetpoint, an ROP setpoint, and a differential pressure setpoint; and arotary drive unit position setpoint.

If the toolface error is indicative that a difference between thetoolface setpoint and the toolface of the downhole tool is less thanabout 90 degrees, then adjusting the selected one or more drillingparameter setpoints may comprise adjusting a rotary drive unit positionsetpoint.

Adjusting the selected one or more drilling parameter setpoints maycomprise adjusting the selected one or more drilling parameter setpointswith one or any combination of: a proportional controller; an integralcontroller; and a derivative controller.

The method may further comprise: determining a difference between adifferential pressure and a differential pressure setpoint; and inresponse thereto, adjusting a rotary drive unit position setpoint basedon the determined difference.

The method may further comprise: determining a rate of change of adifferential pressure; and in response thereto, adjusting a rotary driveunit position setpoint based on the determined rate of change.

According to a further aspect of the disclosure, there is provided asystem for controlling a toolface of a downhole tool, the systemcomprising: a drill string comprising a downhole tool at a downhole endthereof; a drill bit connected to the downhole tool; and a toolfacecontroller for controlling the toolface of the downhole tool, thetoolface controller comprising computer-readable memory and one or moreprocessors, wherein the compute-readable memory comprises computerprogram code configured, when executed by the one or more processors, tocause the one or more processors to perform any of the above-describedmethods.

According to a further aspect of the disclosure, there is provided acomputer-readable medium having stored thereon computer program codeconfigured, when executed by one or more processors, to cause the one ormore processors to perform a method according to any of theabove-described methods.

This summary does not necessarily describe the entire scope of allaspects. Other aspects, features and advantages will be apparent tothose of ordinary skill in the art upon review of the followingdescription of specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate one or more exampleembodiments:

FIG. 1 is a schematic of a drilling rig, according to embodiments of thedisclosure;

FIG. 2 is a block diagram of a system for performing automated drillingof a wellbore, according to embodiments of the disclosure;

FIG. 3 depicts a block diagram of the automatic driller of FIG. 1;

FIG. 4 depicts a block diagram of software modules running on theautomatic driller of FIG. 1;

FIG. 5 depicts a block diagram of a toolface controller interacting withthe automatic driller and top drive controller of FIG. 2, according toembodiments of the disclosure;

FIG. 6 depicts the toolface controller of FIG. 5 adjusting drillingparameter setpoints in a feedback control loop, according to embodimentsof the disclosure;

FIG. 7 depicts a flow diagram of a method of controlling a toolface of adownhole tool, according to embodiments of the disclosure;

FIG. 8 depicts a flow diagram of a further method of controlling atoolface of a downhole tool, according to embodiments of the disclosure;and

FIG. 9 is a plot of off-bottom reactive rotation being introduced as afunction of off-bottom distance separating a drill bit from a bottom ofa wellbore, according to embodiments of the disclosure;

FIG. 10 is a plot of an expected toolface range being adjusted as adrill bit approaches a bottom of a wellbore, according to embodiments ofthe disclosure; and

FIG. 11 is a plot of on-bottom reactive rotation being introduced as afunction of differential pressure increasing toward a differentialpressure setpoint, according to embodiments of the disclosure.

DETAILED DESCRIPTION

The present disclosure seeks to provide improved methods, systems, andcomputer-readable media for controlling a toolface of a downhole tool.While various embodiments of the disclosure are described below, thedisclosure is not limited to these embodiments, and variations of theseembodiments may well fall within the scope of the disclosure which is tobe limited only by the appended claims.

Generally, according to embodiments of the disclosure, there aredescribed methods, systems, and computer-readable media for controllinga toolface of a downhole tool. When the drill bit is off bottom, atoolface controller may cause the drill string to be rotated by a firstamount before the drill bit is determined to have touched bottom, and bya second amount after the drill bit is determined to have touchedbottom. The drill bit may be determined to have touched bottom based ondifferential pressure. The total amount of rotation that is introduced(i.e. the sum of the first and second amounts) may be based on adifference between an initial differential pressure and a differentialpressure setpoint. The first amount of rotation may be introduced, forexample, rapidly (e.g. substantially before the drill bit is determinedto have touched bottom), or gradually as a function of increasing depthof the downhole tool. The second amount of rotation may be introduced,for example, rapidly (e.g. substantially before a differential pressureis determined to have reached a differential pressure setpoint), orgradually as a function of increasing differential pressure.

Subsequently to this initial control of the toolface as the drill bit isbrought to the bottom of the wellbore, the toolface may continue to becontrolled using, for example, a PID feedback controller. Based on acurrent toolface reading and based on a toolface setpoint (correspondingto a desired toolface), the toolface controller may determine which ofmultiple drilling parameter setpoints to adjust in order to control thetoolface. The particular setpoint or setpoints that are adjusted maydepend, for example, on the magnitude of the toolface error (e.g. adifference between the current toolface and the toolface setpoint) aswell as the direction of desired correction to the toolface.

FIG. 1 shows a drilling rig 100, according to one embodiment. The rig100 comprises a derrick 104 that supports a drill string 118. The drillstring 118 has a drill bit 120 at its downhole end, which is used todrill a wellbore 116. A drawworks 114 is located on the drilling rig's100 floor 128. A drill line 106 extends from the drawworks 114 to atraveling block 108 via a crown block 102. The traveling block 108 isconnected to the drill string 118 via a top drive 110. The top drive 110is connected to the drill string 118 by a tubular section known as aquill 111. Rotating the drawworks 114 consequently is able to changeweight-on-bit (WOB) during drilling, with rotation in one directionlifting the traveling block 108 and generally reducing WOB and rotationin the opposite direction lowering the traveling block 108 and generallyincreasing WOB. The drill string 118 also comprises, near the drill bit120, a bent sub 130 and a mud motor 132. The mud motor's 132 rotation ispowered by the flow of drilling mud through the drill string 118, asdiscussed in further detail below, and combined with the bent sub 130permits the rig 100 to perform directional drilling. The top drive 110and mud motor 132 collectively provide rotational force to the drill bit120 that is used to rotate the drill bit 120 and drill the wellbore 116.While in FIG. 1 the top drive 110 is shown as an example rotationaldrive unit, in a different embodiment (not depicted) another rotationaldrive unit may be used, such as a rotary table.

A mud pump 122 rests on the floor 128 and is fluidly coupled to a shaleshaker 124 and to a mud tank 126. The mud pump 122 pumps mud from thetank 126 into the drill string 118 at or near the top drive 110, and mudthat has circulated through the drill string 118 and the wellbore 116return to the surface via a blowout preventer (“BOP”) 112. The returnedmud is routed to the shale shaker 124 for filtering and is subsequentlyreturned to the tank 126.

Uphole of the bent sub 130 is located a measurement-while-drilling (MWD)tool 131. MWD tool 131 collects and transmits data from inside thewellbore 116, such as formation properties, rotational speed, vibration,temperature, torque, pressure, and mud flow. The MWD tool 131 measuresthe inclination, azimuth, and toolface orientation of a downhole toolnear the drill bit 120. Toolface orientation (or simply “toolface”)combined with inclination, azimuth, and the geometry of the bottom holeassembly can be used to determine the trajectory of the drill string118.

The MWD data may be transferred to the surface using any of variousmeans, such as mud pulse telemetry, electromagnetic telemetry (generallyfor relatively shallow depths), acoustic telemetry, or a wired drillpipe. The MWD data is decoded at the surface by an MWD decoder 211.Generally, the decoded MWD data is sent to a directional driller'sworkstation and doghouse computer (see below).

FIG. 2 shows a block diagram of a system 200 for performing automateddrilling of a wellbore, according to the embodiment of FIG. 1. Thesystem 200 comprises various rig sensors: a torque sensor 202 a, depthsensor 202 b, hookload sensor 202 c, and standpipe pressure sensor 202 d(collectively, “sensors 202”).

The system 200 also comprises the drawworks 114 and top drive 110. Thedrawworks 114 comprises a programmable logic controller (“drawworksPLC”) 114 a that controls the drawworks' 114 rotation and a drawworksencoder 114 b that outputs a value corresponding to the current heightof the traveling block 108. The top drive 110 comprises a top driveprogrammable logic controller (“top drive PLC”) 110 a that controls thetop drive's 114 rotation and a revolutions-per-minute (RPM) sensor 110 bthat outputs the rotational rate of the drill string 118. Moregenerally, the top drive PLC 110 a is an example of a rotational driveunit controller and the RPM sensor 110 b is an example of a rotationrate sensor. In addition, top drive 110 further includes a top driverotary encoder 110 c (mounted within or externally to the top drive110). Top drive rotary encoder 110 c is used to measure the angle ofrotation of quill 111. Top drive rotary encoder 110 c is an example of arotational position sensor and is used to provide a feedback signal forcontrolling the toolface of the downhole tool, as described in furtherdetail below.

A first junction box 204 a houses a top drive controller 206, which iscommunicatively coupled to the top drive PLC 110 a, the RPM sensor 110b, and the top drive rotary encoder 110 c. The top drive controller 206controls the rotation rate of the drill string 118 by instructing thetop drive PLC 110 a and obtains the rotational position, rate ofrotation, and direction of rotation of the drill string 118 from topdrive rotary encoder 110 c.

A second junction box 204 b houses an automated drilling unit 208 (orsimply “automatic driller 208”), which is communicatively coupled to thedrawworks PLC 114 a and the drawworks encoder 114 b. The automateddrilling unit 208 modulates WOB during drilling by instructing thedrawworks PLC 114 a and obtains the height of the traveling block 108from the drawworks encoder 114 b. In different embodiments, the heightof the traveling block 108 can be obtained digitally from riginstrumentation, such as directly from the PLC 114 a in digital form. Indifferent embodiments (not depicted), the junction boxes 204 a,204 b maybe combined in a single junction box, comprise part of the doghousecomputer 210, or be connected indirectly to the doghouse computer 210 byan additional desktop or laptop computer.

The automated drilling unit 208 is also communicatively coupled to eachof the sensors 202. In particular, the automated drilling unit 208determines WOB from the hookload sensor 202 c and determines the rate ofpenetration (ROP) of the drill bit 120 by monitoring the height of thetraveling block 108 over time.

The system 200 also comprises a doghouse computer 210. The doghousecomputer 210 comprises a toolface controller 212 and memory 214communicatively coupled to each other. The memory 214 stores on itcomputer program code that is executable by the toolface controller 212and that, when executed, causes the toolface controller 212 to performmethods for performing automated drilling of the wellbore 116. Inparticular, the toolface controller 212 may perform methods forcontrolling a toolface of the downhole tool, such as those shown inFIGS. 7 and 8. The toolface controller 212 receives readings from theRPM sensor 110 b, drawworks encoder 114 b, top drive rotary encoder 110c, and the rig sensors 202. MWD decoder 211, having received a toolfacereading from downhole MWD tool 131, transmits the toolface readingdirectly to toolface controller 212.

The toolface controller 212 sends one or more of an ROP setpoint, adifferential pressure setpoint, and a WOB setpoint to the automateddrilling unit 208, and one or more of an RPM setpoint and a top driveposition setpoint to the top drive controller 206. The top driveposition setpoint may include a rotational position setpoint of the topdrive 110 (indicative of a desired rotational position of the top drive110), or a rotational position setpoint indicative of a target midpointabout which the top drive 110 is oscillated (or a target neutral pointin the case of asymmetric oscillations). The top drive controller 206and automated drilling unit 208 relay these setpoints to the top drivePLC 110 a and drawworks PLC 114 a, respectively, where they are used forautomated drilling.

Each of the first and second junction boxes may comprise a PasonUniversal Junction Box™ (UJB) manufactured by Pason Systems Corp. ofCalgary, Alberta. The automated drilling unit 208 may be a PasonAutodriller™ manufactured by Pason Systems Corp. of Calgary, Alberta.

The top drive controller 206, automated drilling unit 208, and doghousecomputer 210 are respective example types of drilling controllers. Inthe system 200 of FIG. 2, the top drive controller 206206 and theautomated drilling unit 208 are distinct and respectively use the RPMand top drive position setpoints, and the WOB, differential pressure,and ROP setpoints, for automated drilling. However, in differentembodiments (not depicted), the functionality of the top drivecontroller 206 and automated drilling unit 208 may be combined or may bedivided between three or more controllers. In certain embodiments (notdepicted), the toolface controller 212 may directly communicate with anyone or more of the top drive 110, drawworks 114, sensors 202, and MWDdecoder 211. Additionally or alternatively, in different embodiments(not depicted) automated drilling may be done in response to only theRPM setpoint, only the ROP setpoint, only the WOB setpoint, only thedifferential pressure setpoint, only the top drive position setpoint, orany combination thereof, possibly in combination with one or more otherdrilling parameters. Examples of these additional drilling parameterscomprise, for example, depth of cut, torque, and flow rate (into thewellbore 116, out of the wellbore 116, or both).

In the depicted embodiments, the top drive controller 206 and theautomated drilling unit 208 acquire data from the sensors 202 discretelyin time at a sampling frequency F_s, and this is also the rate at whichthe doghouse computer 210 acquires the sampled data. Accordingly, for agiven period T, N samples are acquired with N=TF_s. In differentembodiments (not depicted), the doghouse computer 210 may receive thedata at a different rate than that at which it is sampled from thesensors 202. Additionally or alternatively, the top drive controller 206and the automated drilling unit 208 may sample data at different rates,and more generally in embodiments in which different equipment is useddata may be sampled from different sensors 202 at different rates.

Referring now to FIG. 3, there is shown a hardware block diagram 300 ofthe second junction box 204 b of FIG. 2. The second junction box 204 bcomprises a microcontroller 302 communicatively coupled to a fieldprogrammable gate array (“FPGA”) 320. The depicted microcontroller 302is an ARM-based microcontroller, although in different embodiments (notdepicted) the microcontroller 302 may use a different architecture. Themicrocontroller 302 is communicatively coupled to 32 kB of non-volatilerandom access memory (“RAM”) in the form of ferroelectric RAM 304; 16 MBof flash memory 306; a serial port 308 used for debugging purposes; LEDs310, LCDs 312, and a keypad 314 to permit a driller to interface withthe automatic driller 208; and communication ports in the form of anEthernet port 316 and RS-422 ports 318. While FIG. 3 shows themicrocontroller 302 in combination with the FPGA 320, in differentembodiments (not depicted) different hardware may be used. For example,the microcontroller 302 may be used to perform the functionality of boththe FPGA 320 and microcontroller 302 in FIG. 3; alternatively, a PLC maybe used in place of one or both of the microcontroller 302 and the FPGA320.

The microcontroller 302 communicates with the hookload and standpipepressure sensors 202 c,202 d via the FPGA 320. More specifically, theFPGA 320 receives signals from these sensors 202 c,202 d as analoginputs 322; the FPGA 320 is also able to send analog signals usinganalog outputs 324. These inputs 322 and outputs 324 are routed throughintrinsic safety (“IS”) barriers for safety purposes, and through wiringterminals 330. The microcontroller 302 communicates using the RS-422ports 318 to the PLC 114 a; accordingly, the microcontroller 302receives signals from a block height sensor (not shown) and the torquesensor 202 a and sends signals to a variable frequency drive (or, insome embodiments, a braking device) via the RS-422 ports 318. Accordingto some embodiments, automatic driller 208 outputs a throttle signal toa PLC using an analog output. According to some embodiments, automaticdriller 208 communicates with a band brake controller using an RS-422port.

The FPGA 320 is also communicatively coupled to a non-incendive depthinput 332 and a non-incendive encoder input 334. In differentembodiments (not depicted), the automatic driller 208 may receivedifferent sensor readings in addition to or as an alternative to thereadings obtained using the depicted sensors 202 a,202 b,202 c,202 d.

First junction box 204 a, comprising top drive controller 206, comprisesan input/output architecture similar to that of second junction box 204b shown in FIG. 3. However, the RS-422 port is not used, and all aninputs/outputs use analog or discrete digital signaling.

Referring now to FIG. 4, there is shown a block diagram of softwaremodules, some of which comprise a software application 402, running onthe automatic driller of FIG. 3. The application 402 comprises a datamodule 414 that is communicative with a PID module 416, a block velocitymodule 418, and a calibrations module 420. The microcontroller 302 runsmultiple PID control loops in order to determine the signal to send tothe PLC 114 a to control the variable frequency drive; themicrocontroller 302 does this in the PID module 416. The microcontroller302 uses the block velocity module 418 to determine the velocity of thetraveling block 108 from the traveling block height derived usingmeasurements from the block height sensor. The microcontroller 302 usesthe calibrations module 420 to convert the electrical signals receivedfrom the sensors 202 a,202 b,202 c,202 d into engineering units; forexample, to convert a current signal from mA into kilopounds.

The data module 414 also communicates using an input/output multiplexer,labeled “10 Mux” in FIG. 4. In one of the multiplexer states the datamodule 414 communicates digitally via the Modbus protocol using thesystem modbus 412 module, which is communicative with a Modbusreceive/transmit engine 408 and the UARTS 406. In another of themultiplexer states, the data module 414 communicates analog datadirectly using the data acquisition in/out module 404. While in FIG. 4the Modbus protocol is shown as being used, in different embodiments(not depicted) a different protocol may be used, such as anothersuitable industrial bus communication protocol.

During drilling, a reactive torque is produced by the mud motor 132 thatmay cause the toolface to rotate to the left. Differential pressure maybe used as a proxy for reactive torque. Differential pressure is roughlythe difference between on- and off-bottom standpipe pressure which maybe a proxy for the pressure loss across the mud motor 132. In practice,it is easier to increase differential pressure than to decreasedifferential pressure. In general, it may be preferable to increasedifferential pressure so as to allow drilling rig 100 to drill faster.Increasing differential pressure may generally translate into increasingWOB, resulting in a higher reactive torque. If a leftward toolfacecorrection is required, differential pressure may be increased toproduce a left turn and increased ROP. Using differential pressure forrightward toolface corrections may require reducing differentialpressure, accomplished through drilling off WOB, and may translate intoslower drilling. Therefore, rightward toolface corrections may be betteraccomplished through changes to the rotational position of the top drive110.

Turning to FIG. 5, there is shown a block diagram of toolface controller212 interacting with automatic driller 208, top drive controller 206,and MWD decoder 211. As described in further detail below, toolfacecontroller 212 determines, depending on the desired toolface correction,adjustments to one or more drilling parameter setpoints, and inputs theadjusted drilling parameter setpoint(s) to automatic driller 208 and/ortop drive controller 206 to correct the toolface of the downhole tool,e.g. by minimizing a difference between a measured toolface and thetoolface setpoint (e.g. a desired toolface).

As described above, top drive controller 206 manages the rotation ofdrill string 118, controls the oscillation of drill string 118, andeffects changes to the rotational position of top drive 110. Whenperforming rotational drilling, top drive controller 206 rotates drillstring 118 constantly in the same direction (e.g. to the right). Whensliding, in order to maintain toolface control, top drive controller 206provides changes to one or more of a rotational position of the topdrive 110 and a midpoint (or neutral point) about which the top drive110 is oscillated. Generally, when sliding in the lateral, top drivecontroller 206 oscillates the top of drill string 118 a set amount ineach direction. This reduces friction along drill string 118 and allowsfor smoother sliding. The amount of oscillation is chosen to allow mostof drill string 118 to have some rotation without this rotation reachingthe downhole tool. Changes to the midpoint or neutral point of thisoscillation will propagate to the toolface over time. While oscillationcan be used during vertical drilling and in the build, it is generallymore often used while drilling in the lateral.

MWD decoder 211 receives from MWD tool 131 encoded data relating thetoolface of the downhole tool (e.g. every 30 seconds, for example). MWDdecoder 211 may decode the data to determine the current toolface andprovides the toolface reading to toolface controller 212. MWD decodingcan be performed through a variety of means, depending on how the datais sent. If the data is transmitted using mud-pulse telemetry, then MWDdecoder 211 uses pressure information from a pressure sensor, such asstandpipe pressure sensor 202 d, to identify signals sent through themud. MWD decoder 211 decodes the data and sends the toolface reading totoolface controller 212. The frequency of the updates to the currenttoolface may depend on equipment, conditions, and depth. When a toolfacereading is received from MWD decoder 211, toolface controller 212determines the magnitude of the required correction and determineswhether to correct using automatic driller 208, top drive controller206, or a combination of both. Generally, for small corrections, topdrive controller 206 is used if the correction requires a right turnwhile automatic driller 208 if the correction requires a left turn. Ifthe required correction is large, both top drive controller 206 andautomatic driller 208 may be used. Large corrections and smallcorrections may be defined by the user. For example, according to someembodiments, a large correction may be a correction greater than 90degrees, and, according to some embodiments, a small correction may be acorrection between about 5 degrees and 90 degrees. Toolface controller212 may use a proportional-integral-derivative (PID) controller forcontrolling the toolface.

Turning to FIG. 6, there is shown a feedback control loop forcontrolling, with toolface controller 212, the toolface of the downholetool. A toolface setpoint, corresponding to a desired toolface, is inputby an operator and provided to toolface controller 212. A currenttoolface of drill bit 120 is provided to toolface controller 212 by MWDdecoder 211. WOB, ROP, and differential pressure setpoint ranges arealso provided to toolface controller 212. Based on the toolface setpointand based on the most recent toolface reading provided to toolfacecontroller 212, toolface controller 212 determines a toolface error. Thetoolface error may be indicative of a magnitude of a difference betweenthe toolface reading and the toolface setpoint. Based on the toolfaceerror, toolface controller 212 selects and adjusts one or more drillingparameter setpoints for controlling the toolface, i.e. for reducing amagnitude of a difference between the current toolface and the toolfacesetpoint, as described in further detail below. The drilling parametersetpoints that may be adjusted include a WOB setpoint, a differentialpressure setpoint, an ROP setpoint, and a top drive position setpoint.The WOB, ROP, and differential pressure setpoints may only be adjustedwithin the WOB, ROP, and differential pressure setpoint ranges providedto toolface controller 212.

The adjusted drilling parameter setpoints are input to either, or bothof, automatic driller 208 and top drive controller 206, depending onwhich setpoint or setpoints are adjusted. In particular, adjustments tothe WOB setpoint, the differential pressure setpoint, and the ROPsetpoint are provided to automatic driller 208. Adjustments to the topdrive position setpoint are provided to top drive controller 206. Theadjusted setpoint or setpoints result in appropriate adjustment to thetoolface of the downhole tool. Toolface controller 212 may adjust theone or more drilling parameter setpoints using, for example, aproportional-integral-derivative (PID) control loop, or in some cases aproportional-integral (PI) control loop.

Turning to FIG. 7, there is shown a flow diagram illustrating a methodof controlling the toolface of the downhole tool, using toolfacecontroller 212, according to embodiments of the disclosure.

At block 702, a toolface of the downhole tool is determined. Forexample, the most recent toolface reading sent from MWD decoder 211 totoolface controller 212 may be used for determining the currenttoolface. At block 704, a toolface setpoint is determined. The toolfacesetpoint may be whatever setpoint is provided to toolface controller 212by the operator. At block 706, toolface controller 212 determines atoolface error. The toolface error may be determined based on one ormore differences (e.g. magnitude, direction) between the currenttoolface and the toolface setpoint.

At block 708, toolface controller 212 determines whether the toolfaceerror is large or small. The difference between a large toolface errorand a small toolface error may be configured by the operator, forexample. According to some embodiments, a toolface error between about 5degrees and about 90 degrees may constitute a small toolface error,while a toolface error greater than about 90 degrees may constitute alarge toolface error.

If the toolface error is considered to be small, then, at block 710,toolface controller 212 determines whether the required correction is tothe left or to the right. If the required correction is to the left,then, at block 712, toolface controller 212 adjusts one or more of theWOB setpoint, the differential pressure setpoint, and the ROP setpoint.At block 714, toolface controller 212 inputs the adjusted one or moredrilling parameter setpoints to automatic driller 208.

If the required correction is to the right, then, at block 716, toolfacecontroller 212 adjusts the top drive position setpoint. At block 718,toolface controller 212 inputs the adjusted top drive position setpointto top drive controller 206.

If on the other hand the toolface error is considered to the large,then, at block 720, toolface controller 212 adjusts one or more of theWOB setpoint, the differential pressure setpoint, and the ROP setpoint,and additionally adjusts the top drive position setpoint. At block 722,toolface controller 212 inputs the adjusted drilling parameter setpointsto both automatic driller 208 and to top drive controller 206.

When correcting to the left, the intent as explained above is toincrease the differential pressure. The most efficient way ofaccomplishing this may be is dependent, for example, on the automaticdriller 208, the current formation being drilled, and/or userpreference. A common case is as follows. If toolface controller 212determines that the differential pressure may be safely increased (e.g.the current differential pressure is relatively close to thedifferential pressure setpoint, and is stable), if the WOB, ROP, anddifferential pressure setpoints are not at their maximum allowablevalues, and if the toolface error is considered small (as per above),then toolface controller 212 will increase the differential pressuresetpoint. In addition, toolface controller 212 will adjust the WOBsetpoint and optionally the ROP setpoint to enable the differentialpressure to increase toward the new differential pressure setpoint. Themagnitude of the setpoints increases will depend on various factors,such as on or more of: proportional, integral, and derivative valuesassociated with the toolface error, pre-set gains, gains dependent onuser input (such as ReactiveT_Factor—see below), gains dependent onanalysis of the history of the relationship between toolface anddifferential pressure, and both pre-set and user-adjusted minimum andmaximum allowable values.

Toolface controller 212 may additionally perform a differential pressurecompensation operation, for example at regular intervals. Whenperforming the differential pressure compensation operation, toolfacecontroller 212 determines a difference between the current differentialpressure and the differential pressure setpoint, as well as a rate ofchange of differential pressure relative to the differential pressuresetpoint. Based on the difference between the current differentialpressure and the differential pressure setpoint, as well as the rate ofchange of differential pressure relative to the differential pressuresetpoint, toolface controller 212 may adjust the top drive positionsetpoint. The amount by which the top drive position setpoint isadjusted may be of the form(DiffP−DiffP_Setpoint)*ReactiveT_Factor*Scaling_Factor. In addition, oralternatively, the amount by which the top drive position setpoint isadjusted may be of the formDiffP_Derivative*ReactiveT_Factor*Scaling_Factor. ReactiveT_Factor is aconstant that defines a relationship between differential pressure andpipe twist (e.g. 90 degrees per 1,000 kPa), and is an approximation ofthe spring constant of the pipe. ReactiveT_Factor and Scaling_Factor aregenerally user-entered and reflect, for a given differential pressure,the amount the top drive has to be rotated in order to maintain a stabletoolface. By performing the differential pressure compensationoperation, toolface controller 212 smooths changes in differentialtorque. Since it may take a significant amount of time for any change atthe surface to reach the toolface, this input is scaled usingScaling_Factor, with the intention being that, over time, theadjustments will stabilize the toolface. In general, when sliding, ROPis low (1-50 m/h with a typical speed of 8-10 m/h) and it may takeseveral minutes for an adjustment to propagate downhole.

If multiple processes (toolface control, differential pressurecompensation, and/or other currently available or future developedprocesses) require concurrent changes to be sent to automatic driller208 and/or top drive controller 206, their outputs are summed.

Separate to ongoing toolface control, toolface controller 212 controlshow and when compensation for reactive torque is introduced to the drillstring 118 when drill bit 120 is going to bottom. This can occur, forexample, after a connection, after switching from rotational drilling toslide drilling, when toolface control is lost and drill bit 120 israised from the bottom to re-establish toolface control, or whentoolface control is halted to allow WOB to drill off. As drill bit 120nears the bottom of the wellbore, a first amount of the total desiredrotation of drill string 118 is added by top drive controller 206, andthe remainder of the total desired rotation is added after drill bit 120touches bottom. According to some embodiments, about 80% of the totaldesired rotation is added before drill bit 120 touches bottom. The pointat which drill bit 120 touches bottom may be detected based ondifferential pressure alone, or based on a combination of differentialpressure and one or more comparisons of bit depth and hole depth.Differential pressure, instead of bit/hole depth, is used to determinecontact, as instead of bit/hole depth may be inaccurate and can beaffected by pipe stretch. The timing of the introduction of rotation ofdrill string 118 is based on off-bottom distance and differentialpressure, or based on a distance drilled since touching bottom.

Turning to FIG. 8, there is shown a flow diagram illustrating a methodof controlling a toolface when a drill bit is off-bottom and going tobottom, according to embodiments of the disclosure.

At block 802, toolface controller 212 determines whether drill bit 120is off bottom. For example, toolface controller 212 may determine thatdrill bit 120 is off bottom if a current depth of drill bit 120 as readby a suitable depth sensor is less than a depth of the wellbore, and ifthe current differential pressure is greater than 0. If drill bit 120 isdetermined to not be off bottom (e.g. the drill bit is on bottom), thenthe process may proceed to block 826 where on-bottom toolface control isperformed. For example, when performing on-bottom toolface control, thetoolface may be controlled using the method described above inconnection with FIG. 7. If drill bit 120 is determined to be off bottom,then the process proceeds to block 804. In addition, the differentialpressure setpoint may be initialized by using either the currentdifferent pressure setpoint or, if none is available, then setting thedifferential pressure setpoint to the current reactive pressure reading.

At block 804, toolface controller 212 determines the total reactiverotation that is required. The total reactive rotation that is requiredmay be determined according to (DiffP_Setpoint−DiffP)*ReactiveT_Factor,where ReactiveT_Factor is the number of degrees of rotation required perunit of kPa (this constant may be set by the operator or may becalculated on the fly) to counteract the expected change in toolface asdrill bit 120 moves to the bottom of the wellbore.

At block 806, toolface controller 212 adjusts the top drive positionsetpoint by an amount corresponding to the initial toolface error (e.g.the difference between the current toolface and the toolface setpoint).At block 808, toolface controller 212 determines an expected toolfacerange. The expected toolface range may be defined as the differencebetween the current toolface and the toolface setpoint, and correspondsto a range within which it is expected that the toolface will vary asdrill bit 120 moves to the bottom of the wellbore.

At block 810, toolface controller 212 determines whether the currenttoolface is outside of the expected toolface range and, if so, thentoolface controller 212 adjusts the top drive position setpoint so as tosteer the toolface toward the expected toolface range. When the toolfaceis determined to be outside of the expected toolface range, the expectedtoolface range is widened accordingly to encompass the current toolfacereading. Block 810 may be repeated until the method of FIG. 8 iscompleted. FIG. 9 is a plot showing adjustments to the expected toolfacerange as the drill bit 120 approaches the bottom of the wellbore. Theexpected toolface range is adjusted both in response to reactiverotation that is introduced into drill string 118 as well as in responseto the current toolface being determined to be outside of the expectedtoolface range. The “initial bump” shown in FIG. 9 corresponds to theadjustment of the top drive position setpoint by the amountcorresponding to the initial toolface error (block 806).

At block 812, toolface controller 212 introduces a first amount (i.e. anoff-bottom amount) of reactive rotation into drill string 118, byadjusting the top drive position setpoint. In particular, as bit depthincreases (i.e. as drill bit 120 approaches the bottom of the wellbore),the top drive position setpoint is further adjusted in a constantdirection in order to rotate drill string 118. The total amount ofoff-bottom rotation that drill string 118 undergoes depends on thefraction of the total required reactive rotation (as determined at block804) that the operator wishes to introduce before drill bit 120 isdetermined to have touched bottom vs. the fraction of the total requiredreactive rotation that the operator wishes to introduce after drill bit120 is determined to have touched bottom. FIG. 10 shows an example ofoff-bottom reactive rotation being introduced proportionally to bitdepth. According to some embodiments, instead of the off-bottom reactiverotation being introduced gradually as a function of bit depth, theoff-bottom reactive rotation may be introduced independently of bitdepth, and in some cases may be introduced rapidly, before drill bit 120is determined to have touched bottom.

At block 814, toolface controller 212 determines whether thedifferential pressure has reached a predetermined differential pressurethreshold. The predetermined differential pressure threshold may be, forexample, a fraction of the difference between the differential pressuresetpoint and the current differential pressure. According to someembodiments, the differential pressure threshold may be 25% of thedifference between the differential pressure setpoint and the currentdifferential pressure. If the current differential pressure reading hasnot yet reached the predetermined differential pressure threshold, thenthe process returns to block 812. Otherwise, if the current differentialpressure reading has reached the predetermined differential pressurethreshold, then, at block 816, toolface controller 212 determines that atouchdown condition is met, and that drill bit 120 has touched bottom.

After drill bit 120 is determined to have touched bottom, then, at block818, toolface controller 212 introduces a second amount (i.e. anon-bottom amount) of reactive rotation into drill string 118, by furtheradjusting the top drive position setpoint. In particular, asdifferential pressure increases toward the differential pressuresetpoint, the top drive position setpoint is further adjusted in aconstant direction in order to further rotate drill string 118. Thetotal amount of on-bottom rotation that drill string 118 undergoesdepends on the fraction of the total required reactive rotation (asdetermined at block 804) that the operator has introduced before drillbit 120 is determined to have touched bottom. FIG. 11 shows an exampleof on-bottom reactive rotation being introduced proportionally todifferential pressure. Generally, the proportion of off-bottom reactiverotation to on-bottom reactive rotation is variable and may be based forexample on user-preference and hole depth. Generally, for deeper holes,the proportion of off-bottom reactive rotation to on-bottom reactiverotation increases, as it takes longer for rotation introduced atsurface to propagate downhole.

At block 820, toolface controller 212 determines whether the currentdifferential pressure has reached the differential pressure setpoint.Toolface controller 212 ensures that all of the on-bottom reactiverotation is introduced to drill string 118 by the time the differentialpressure has reached the differential pressure setpoint. If the currentdifferential pressure has not yet reached the differential pressuresetpoint, then the process returns to block 818. In response todetermining that the current differential pressure has reached thedifferential pressure setpoint, then, at block 822, toolface controller212 increases the differential pressure setpoint such that itcorresponds to a reactive pressure value. The reactive pressure value isentered by the user as part of the above pipe twist calculation. Atblock 822, the differential pressure setpoint, which had previously beenset below the reactive pressure value, is made equal to the reactivepressure value. If the differential pressure setpoint is the same as thereactive pressure, this increase is nil. Setting the differentialpressure setpoint equal to the reactive pressure value sets thedifferential pressure setpoint at a known, desired operating value. Inorder to compensate for this further increase in the differentialpressure setpoint, at block 824, toolface controller 212 further adjuststhe top drive position setpoint to further rotate drill string 118.

The process then proceeds to block 826 where control of the toolfaceproceeds with the on-bottom toolface control described above inconnection with FIG. 7.

Various parameters may be adjusted in the method described above inconnection with FIG. 8. For example, one or more of the followingparameters may be adjusted:

-   -   the proportions of the total required reactive rotation that are        introduced before and after the differential pressure has        reached the differential pressure threshold (indicative of the        touchdown condition having been met);    -   the distance separating drill bit 120 and the bottom of the        wellbore before off-bottom reactive rotation begins to be        introduced;    -   the distance separating drill bit 120 and the bottom of the        wellbore before off-bottom reactive rotation stops being        introduced;    -   the fraction of the differential pressure rise toward the        differential pressure setpoint before on-bottom reactive        rotation begins to be introduced; and    -   the difference between the differential pressure and the        differential pressure setpoint before on-bottom reactive        rotation stops being introduced.

Furthermore, according to some embodiments, toolface controller 212 mayfurthermore monitor a toolface error adjustment value of the formTF_err_adj=TF_err+expected_future_TFDelta. As differential pressurerises, the value of expected_future_TFDelta (the expected future changein toolface in response to the change in differential pressure) willchange. Thus, if the toolface is expected to change in a direction thatis desired (i.e. that will reduce the toolface error), then the toolfacecontroller may avoid adjusting the toolface setpoint and/or the topdrive position setpoint in anticipation of the toolface error reducingas differential pressure increases. Thus, active steering of thetoolface may be avoided in favour of the toolface adjusting naturally asa result of the increase in differential pressure. Likewise, if thetoolface is expected to change in a direction that is not desired (i.e.that will increase the toolface error), then the toolface controller mayprovide more active steering by further adjusting the toolface setpointand/or the top drive position setpoint in anticipation of the toolfaceerror increasing.

The word “a” or “an” when used in conjunction with the term “comprising”or “including” in the claims and/or the specification may mean “one”,but it is also consistent with the meaning of “one or more”, “at leastone”, and “one or more than one” unless the content clearly dictatesotherwise. Similarly, the word “another” may mean at least a second ormore unless the content clearly dictates otherwise.

The terms “coupled”, “coupling” or “connected” as used herein can haveseveral different meanings depending on the context in which these termsare used. For example, the terms coupled, coupling, or connected canhave a mechanical or electrical connotation. For example, as usedherein, the terms coupled, coupling, or connected can indicate that twoelements or devices are directly connected to one another or connectedto one another through one or more intermediate elements or devices viaan electrical element, electrical signal or a mechanical elementdepending on the particular context. The term “and/or” herein when usedin association with a list of items means any one or more of the itemscomprising that list.

As used herein, a reference to “about” or “approximately” a number or tobeing “substantially” equal to a number means being within +/−10% ofthat number.

While the disclosure has been described in connection with specificembodiments, it is to be understood that the disclosure is not limitedto these embodiments, and that alterations, modifications, andvariations of these embodiments may be carried out by the skilled personwithout departing from the scope of the disclosure.

It is furthermore contemplated that any part of any aspect or embodimentdiscussed in this specification can be implemented or combined with anypart of any other aspect or embodiment discussed in this specification.

1. A method of controlling a toolface of a downhole tool, comprising:when a drill bit is off-bottom relative to a wellbore: determining atotal amount of rotation to be introduced to a drill string connected tothe drill bit; and performing a first toolface control operationcomprising rotating the drill string by an off-bottom amount ofrotation; measuring a differential pressure; determining, based on themeasured differential pressure exceeding a threshold, that a touchdowncondition has been met; and in response to determining that thetouchdown condition has been met, performing a second toolface controloperation comprising further rotating the drill string by an on-bottomamount of rotation, wherein the total amount of rotation is equal to asum of the off-bottom and on-bottom amounts of rotation.
 2. The methodof claim 1, wherein rotating the drill string comprises adjusting arotary drive unit position setpoint corresponding to a desired positionof a rotary drive unit operable to rotate the drill string.
 3. Themethod of claim 2, wherein the rotary drive unit position setpointcomprises a top drive position setpoint, and wherein the rotary driveunit comprises a top drive.
 4. The method of claim 1, whereindetermining the total amount of rotation comprises: determining adifference between a differential pressure setpoint and an initialdifferential pressure; and determining the total amount of rotationbased on the determined difference.
 5. The method of claim 1, whereinthe off-bottom amount of rotation is at least as large as the on-bottomamount of rotation.
 6. The method of claim 1, further comprising, beforeperforming the first toolface control operation, rotating the drillstring by an initial amount of rotation.
 7. The method of claim 6,further comprising: before performing the first toolface controloperation, determining an initial toolface of the downhole tool; anddetermining a toolface setpoint, wherein the initial toolface and thetoolface setpoint define an expected toolface range; and furtherrotating the drill string if the toolface of the downhole tool isdetermined to be outside of the expected toolface range.
 8. The methodof claim 1, wherein performing the second toolface control operationcomprises further rotating the drill string by the on-bottom amountproportionally to increasing differential pressure.
 9. The method ofclaim 1, further comprising: after performing the second toolfacecontrol operation, determining that a depth of the drill bit correspondsto a depth of the wellbore; and in response to determining that thedepth of the drill bit corresponds to the depth of the wellbore,performing a third toolface control operation comprising furtherrotating the drill string.
 10. The method of claim 10, whereinperforming the third toolface control operation comprises: increasing adifferential pressure setpoint such that the differential pressuresetpoint corresponds to a reactive pressure; and further rotating thedrill string based on the increased differential pressure setpoint. 11.The method of claim 1, further comprising, after performing the secondtoolface control operation: determining a toolface error based on adifference between the toolface of the downhole tool and a toolfacesetpoint; adjusting, based on the toolface error, one or more drillingparameter setpoints; and inputting the one or more adjusted drillingparameter setpoints to one or more drilling controllers for controllingthe toolface of the downhole tool.
 12. The method of claim 11, whereinadjusting the one or more drilling parameter setpoints comprises:selecting, based on the toolface error, one or more drilling parametersetpoints from among multiple drilling parameter setpoints; andadjusting the selected one or more drilling parameter setpoints.
 13. Amethod of controlling a toolface of a downhole tool, comprising:determining the toolface of the downhole tool; determining a toolfacesetpoint; determining, based on the toolface and the toolface setpoint,a toolface error; selecting, based on the toolface error, one or moredrilling parameter setpoints from among multiple drilling parametersetpoints; adjusting the selected one or more drilling parametersetpoints; and inputting the adjusted one or more drilling parametersetpoints to one or more drilling controllers for controlling thetoolface of the downhole tool.
 14. The method of claim 13, wherein thetoolface error is indicative of one or more of: a magnitude of adifference between the toolface and the toolface setpoint; and adirection of a difference between the toolface and the toolfacesetpoint.
 15. The method of claim 13, wherein the one or more drillingparameter setpoints comprise one or more of: a weight-on-bit (WOB)setpoint; a differential pressure setpoint; a rate of penetration (ROP)setpoint; and a rotary drive unit position setpoint.
 16. The method ofclaim 15, wherein: the one or more drilling controllers comprise one ormore of an automated drilling unit and a rotary drive unit controller;and inputting the adjusted one or more drilling parameter setpoints tothe one or more drilling controllers comprises: inputting the adjustedone or more drilling parameter setpoints to the automated drilling unitif the one or more drilling parameter setpoints comprise one or more ofa WOB setpoint, an ROP setpoint, and a differential pressure setpoint;and inputting the adjusted one or more drilling parameter setpoints tothe rotary drive unit controller if the one or more drilling parametersetpoints comprise a rotary drive unit position setpoint.
 17. The methodof claim 13, wherein: if the toolface error is indicative that thetoolface setpoint is located in a counter-clockwise direction relativeto the toolface of the downhole tool, selecting the one or more drillingparameter setpoints comprises selecting one or more first drillingparameter setpoints from among the multiple drilling parametersetpoints; and if the toolface error is indicative that the toolfacesetpoint is located in a clockwise direction relative to the toolface ofthe downhole tool, selecting the one or more drilling parametersetpoints comprises selecting one or more second drilling parametersetpoints from among the multiple drilling parameter setpoints.
 18. Themethod of claim 13, wherein: if the toolface error is indicative thatthe toolface setpoint is located in a counter-clockwise directionrelative to the toolface of the downhole tool, adjusting the selectedone or more drilling parameter setpoints comprises adjusting one or moreof a WOB setpoint, an ROP setpoint, and a differential pressuresetpoint; and if the toolface error is indicative that the toolfacesetpoint is located in a clockwise direction relative to the toolface ofthe downhole tool, adjusting the selected one or more drilling parametersetpoints comprises adjusting a rotary drive unit position setpoint. 19.The method of claim 13, wherein, if the toolface error is indicativethat a difference between the toolface setpoint and the toolface of thedownhole tool is greater than about 90 degrees, adjusting the selectedone or more drilling parameter setpoints comprises adjusting: one ormore of a WOB setpoint, an ROP setpoint, and a differential pressuresetpoint; and a rotary drive unit position setpoint.
 20. The method ofclaim 13, wherein, if the toolface error is indicative that a differencebetween the toolface setpoint and the toolface of the downhole tool isless than about 90 degrees, adjusting the selected one or more drillingparameter setpoints comprises adjusting a rotary drive unit positionsetpoint.
 21. The method of claim 13, further comprising: determining adifference between a differential pressure and a differential pressuresetpoint; and in response thereto, adjusting a rotary drive unitposition setpoint based on the determined difference.
 22. The method ofclaim 13, further comprising: determining a rate of change of adifferential pressure; and in response thereto, adjusting a rotary driveunit position setpoint based on the determined rate of change.
 23. Acomputer-readable medium having stored thereon computer program codeconfigured, when executed by one or more processors, to cause the one ormore processors to perform a method of controlling a toolface of adownhole tool, comprising: when a drill bit is off-bottom relative to awellbore: determining a total amount of rotation to be introduced to adrill string connected to the drill bit; and performing a first toolfacecontrol operation comprising rotating the drill string by an off-bottomamount of rotation; measuring a differential pressure; determining,based on the measured differential pressure exceeding a threshold, thata touchdown condition has been met; and in response to determining thatthe touchdown condition has been met, performing a second toolfacecontrol operation comprising further rotating the drill string by anon-bottom amount of rotation, wherein the total amount of rotation isequal to a sum of the off-bottom and on-bottom amounts of rotation. 24.A computer-readable medium having stored thereon computer program codeconfigured, when executed by one or more processors, to cause the one ormore processors to perform a method of controlling a toolface of adownhole tool, comprising: determining the toolface of the downholetool; determining a toolface setpoint; determining, based on thetoolface and the toolface setpoint, a toolface error; selecting, basedon the toolface error, one or more drilling parameter setpoints fromamong multiple drilling parameter setpoints; adjusting the selected oneor more drilling parameter setpoints; and inputting the adjusted one ormore drilling parameter setpoints to one or more drilling controllersfor controlling the toolface of the downhole tool.